1. Field of the Invention
This invention relates to a three dimensional display system and, more specifically, to a system capable of displaying images on a screen in three dimensions wherein one or more such images can be projected in two dimensions from either the same side of the screen or from opposite sides thereof.
2. Brief Description of the Prior Art
It has been known in the prior art to modulate or scan a beam, such as a laser beam and then to project the scanned beam onto a screen. Examples of such systems are set forth in Baker U.S. Pat. Nos. 3,471,641 and 3,549,800.
It has also been long desired to provide a three dimensional display. Prior art systems for creating such a display have involved moving a flat plate mirror or flexing a plastic mirror to reflect a CRT image to create a volume display. Similar techniques have employed a Mylar membrane stretched over a metal ring and silvered on the from surface, such mirror being vibrated to reflect the information displayed on the CRT in synchronism with the mirror motion. Such techniques and techniques for converting a cathode ray tube two dimensional display into a three dimensional image are discussed in the article "Terminal Puts 3-Dimensional Graphics on Solid Ground", by Harry S. Stover, Electronics, Jul. 28, 1961.
Prior art three dimensional display techniques were limited because of their use with CRT screens in that the produced image may be viewed only from selected angles. Moreover, such prior art systems have generally not been able to produce real time images and have been limited in the possible vibration frequencies of the screens. Moreover, the use of vibrating mirrors has created difficulties due to the relatively large mass of the mirrors which prevent substantial deflections. For example, such prior art systems have generally been capable of providing a mirror displacement of about 0.4 millimeters.
A need thus arose for a simple and economical three dimensional display system that could produce substantial displacement at a variety of frequencies in order to provide three dimensional images which can be view from all angles. A system which solved this problem is disclosed in Sher U.S. Pat. No. 4,130,832 wherein the three dimensional display includes a laser which directs a beam of light toward a mirror, the mirror being moved In an X-Y plane by piezoelectric transducers. The reflected light beam is directed to a vibrating screen which is moved by a piezoelectric transducer to form a three dimensional image. This system, while providing the desired result, is limited as to the size of the image displayed since the screen and image size are determined by the size of the piezoelectric transducer. Also, this system is affected by G forces, thereby presenting problems where such forces exist, such as in aircraft. The above noted prior art is incorporated herein by reference. In addition, U.S. Pat. Nos. 1,794,103, 3,682,553 and 3,970,361 set forth typical prior art displays of the above noted type.